Combustion control system



May 5, 1942. M. J. MAYNARD COMBUSTION CONTROL SYSTEM Filed Nov. 25, 1938 fi/ 7 A: M attorney,

Patented Ma 1942 OFFICE,

COMBUSTION couraor. srsram Meade J. Maynard, Minneapo 11!, Min, assignmto Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application November 25, 1938, Serial No. 242,2

6 Claims.

My invention relates to the control of heating apparatus employing forced draft and is particularly concerned with improved safety devices for controlling draft in relation to fuel supply in a manner to insure that those practicing my invention will be exempt from the usual hazards attendant to the use of gas and oil fired heating equipment and various other types of equipment fired with fuel burned under forced draft. Most important among these hazards is, of course, the danger of introducing an igniter such as a spark or flame into a combustion chamber which has not been properly scavenged and which may be filled with explosive material in the form of gas fumes or air laden with minute particles of pulverized solid fuel suspended therein. v

The primary object of my invention is to provide improved apparatus for insuring that the draft is always initiated ahead of the fuel supplying means equipment of the above type and is always properly maintained while fuel is being supplied to the equipment.

Another object is to provide an improved device for insuring that the proper sequence and maintenance of draft and fuel supply are effected and which can only fail safe, that is, in the event of any casualty to the device itself or otherwise resulting in draft failure, shut down of the system is always eflected according to a sequence maintaining immunity from various dangers and hazards usually characteristic of the type of equipment to which my invention relates.

A further object is the provision of a fuel supply control device responsive to draft comprising a heat actuated switch arranged to shut oil the fuel supply in the event of draft failure or of a contingency otherwise changing the amount of heatreaching the switch.

A further object is the provision of a draft responsive device comprising a draft tube having a heater and a heat actuated switch therein arranged so that the draft carries heat to the switch for actuating it.

Another objectis the provision of a temperature control system wherein the fuel'supply means are controlled by a heat actuated switch, heat for actuating the switch being carried to it by draft so that if draft fails the fuel supply means are shut down.

Another object is the provision of a fuel control system having a draft responsive fuel control device actuated by heat and arranged so that in a manner and o nects with the one space: or rooms to be heated, the distributing draft air conveys heat away from the device for actuating it.

Other objects and advantages of my invention will become apparent from the accompanying drawing and detailed specification following.

Figure l of warm air heating system having a, preferred form of my improved control arrangement embodied therein. v

Figure 2 is a modified form of my invention.

Referring to Figure l of the drawing, at i I have indicated a warm air furnace having a combustion chamber 2 and a jacket 8 forming a bonnet for the furnace within which air is heated for use in rooms or spaces being served. A stack or flue s M": with the combustion chamber 2 and an air distributing duct 5 conbonnet 3 ior conveying air to variduct 6 having branch ducts the duct 6 communicating rooms. Air is returned from the rooms or spaces and recirculated through the furnace by means oi a return air duct i communicating'with the lower part of the jacket 8. r V

Disposed within the combustion chamber 2 is a conventional gas burner it and fuel is supplied thereto through a conduit H which may be connected to a gas supply main. Interposed in the conduit ii is a fuel controlvalve l2 whichmay be an electric solenoid type valve as I have shown, or it may take the form, of other known fuel control valves now in use. For igniting fuel supplied or passages such as with the individual to the burner it is a constantly burning pilot burner it which may through a tube it connected to the conduit il ahead of the valve i2. interposed in the tube it is a small electric solenoid type valve i5 and connected to the tube It in by-pas's relation with the valve i5 is a small by-pass tube I6. Fuel is continually supplied to the valve i3 through the conduit ii through the tube M, the by-pass i6 and the continuation of the tube It. Whenever heat within the combustion chamber 2 is to be initiated be supplied with fuel as will presently be described, the valve I 5 .is opened so that fuel may be supplied directly through the tube it to the pilot burner as well as through the by-pass It. The tube It is larger than the by-pass. it so that when the valve I5 is open the size of the pilot flame is augmented to insure that it will be sumciently large to ignite the fuel supplied to the burner l0.

Arranged adjacent the flame of the pilot burner i3 is a safety pilot. I 9 which may be of conventional type comprising the drawing represents a gas fired a bimetal blade 20 which 24. Numeral 25 indicates generally a draft rel2. The device 25 in the complete an electrical circuit Upon failure-or discontinuance of the supply of times when there is the switch formed by the is normally heated by the flame of the pilot fixed electrical contact 2|. for scavenging the burner and engages a Draft for combustion and which communicates with the combustion chamber by means of a conduit The fan 22 is driven by an electric motor sponsive control device for controlling the valve form in which I have chosen to disclose it comprises a Pitot tube 23 having an orifice 2'! in tending within the conduit 23, the tube and oriflce being so arranged that when the fan 22 is in operation, draft air is forced through the orifice 21 and into the tube 26. Disposed within the tube 26 is an electric heating resistance 28 and a bimetal switch blade 29 cooperating with a fixed electrical contact 30. Between the heater 23 and thermal switch formed by switch blade 29 is a small bafie 3| interposed in the path of air flowing downwardly through the tube 23. I Whenever the heater 28 is energized and draft is being properly supplied through the conduit 23, air will be forced downwardly through the tube 23 and will carry sumclent heat from the heater 28 to the bimetal blade 29 to cause the blade to flex into engagement with the contact 33 and therethrough.

draft through the conduit 23 the downward circulation of air through the tube 26 will stop and heat will no longer be carried to the blade 29 so that it will assume its original position and break contact with the fixed contact 30. At no pressure in the conduit 23, that is, when the draft fan 22 is not operating, the chimney efieot of the tube 26 will cause air to circulate upwardly therethroughrather than downwardly as takes place when the fan 22 is operating. The natural tendency of warm air tube 26 by reason of the heat at heater 28 when there is no pressure in conduit 23 for enforcing a downward circulation through tube 26.

Primary control of my system is exercised by through the combustion chamber 2 for scavenga portion of the tube exing it to remove any combustible gases which may have accumulated therein and which may have remained in an unburned state while. the apparatus was not in operation. Opening of the small valve I 5 admits an additional quantity of gas to the burner i3 for increasing the size of the pilot flame to insure ignition at the burner it when gas is suppplied thereto.- If operation of the fan 22 is properly initiated and heater 28 is properly energized as described, heat will be carried from the heater downwardly through tube 25 and switch blade 29 will be flexed into vto rise will cause an upward circulation of air in a space thermostat 33 which may be of conven- Q tional type comprising a bimetal element 3% arranged to actuate a switch blade 35 cooperating with a fixed electrical contact 35. The blade 35 cooperates with a permanent magnet 31 which imparts snap opening and closing movements to blade 35 and contact 36.

In operation when the temperature of the space being heated falls to a predetermined value, the blade 35 of thermostat 33 engages with fixed contact 36 and completes electrical circuits energizing the fan motor 24, the heater 28 and the small pilot control valve I5. Numerals 38 and 39 designate line conductors connected to a su table source of external power and when the thermostat closes, the electrical circuit for the'fan motor 24 is as follows: from line conductor 33 through the thermostat blade35, fixed contact 33 wire 40, fan motor 24, wire 4|, back to line conductor 39. The circuit for the heater 28 is from line conductor'38 through fixed contact 36, wire 40, wire 42, heater 28, wire 43, and wire 4| back to line conductor 39. The circuit for the small valve I5 is from line conductor 38 through contact 36, wire 40, wire 44, valve l5, wire 45,j

described the as 22 is the thermostat blade 35,

thermostat blade 35, fixed started in operation for enforcing a circulation] engagement with fixed contact 33. Upon this occurring a circuit for energizing and opening the valve i2 is completed as follows: from line conductor 33 through thermostat blade 35, fixed contact 35, wire til, wire 31, blade 29, fixed contact 33, wire 38, valve l2, wire 49, safety pilot l3, wire 5|! back to line conductor l9. Upon completion of this latter circuit, the main valve i2 opens admitting gas to the burner l0 which is ignited by the fiame of the pilot burner l3 and heating is initiated within the combustion chamber 2. Heating will continue under the control of thermostat 3 and the draft responsive device 25. If draft should fail for any reason whatever while the heating apparatus is in operation, the draft responsive device 25 will operate to deenergize the valve I2 and shut down the system. For example, if the motor 24 driving the fan within conduit 23 to drop, sufficient heat would no longer be carried to the blade 23 for causing it to flex into engagement with the fixed contact 30. Thus the above described circuit for valve I2 would be interrupted andthe supply of gas to burner l3 would be discontinued so as to safely shut down the system. If for some reason the heater 28 should become defective so that it should fail to properly supply heat, the blade 29 would flex away from the contact 30 in the samemanner and'also shut down the system. Thus it is to be seen that the draft responsive device 25 is arranged so that in the event of any type of failure or the occurrence of any exigency as might otherwise bring about a dangerous condition, the draft device 25 will bring about shutdown of the system in a safe' manner. This represents an safety switch to as- .sume a closed rather than an open position which is undesirable. Y Whenever the thermostat 33 becomes satisfied, all of the above described circuits will be interrupted thus closing both the valves l5 and I2 and stopping the fan22 and deenergizing the heater 28. It is to be seen that when-heating is initiated the valve I2 is not opened until after draft has properly been established through the combustion chamber 2 but when heating is to be terminated the valve I2 is immediately closed in response to the opening of thermostat 33. At times when the apparatus is not in operation, the valve I5 is closed and only a very small amount of gas is supplied to the burner l3 through the by-pass it. Thus the amount of fuel consumed when heating is not required is very small and economical.

Referring to Figure 2 of the drawing wherein I have disclosed a second form of my invention,

the same but the draft responsive device is of improvement in the art inasmuch as in known devices certain types of failure of A the apparatus will cause the 22 should fail causing the pressure a slightlydifferent character and operates in a slightly different manner. The elements of Figure 2 which differ from the disclosure of Figure 1 are numbered with numbers greater than 100. It will be noted that in Figure 2 the draft responsive device comprises a mercury switch H9 actuable by a helical thermostatic element I29 disposed in the path of draft air in the conduit 23. Arranged within the helical thermostatic element I29 is the electrical heating resistance 28 which in this form of the invention is continuously energized through an electrical circuit from line conductor 38, wire I42, heater 28, wire I43 back to line conductor 39. In operation, when the thermostat 33 of Figure 2 closes indicating a need for heating, a circuit for energizing the fan motor 24 is completed as follows: from line conductor 38 through thermostatic blade 35, fixed contact 36, wire 40, motor 24, wire 4| back to line conductor 39. At the same time a circuit for energizing the small electric valve I5 is completed as follows: from line conductor 98 through thermostatic blade v35, fixed contact 36, wire 40, wire 44, valve I5, wire 45,

and wire 4| back to line conductor 39. Upon completion of the above circuits the draft fan 22 is started in operation and the small fuel valve I5 is opened, it being understood that the switch H8 controls the valve I2 and is normally in an open position under the influence of heat from heater 28 acting upon element I29. As

soon as draft has properly been established through conduit 23 and the combustion chamber of the furnace a large part of the heat generated by element 28 will be carried away by the draft air and the draft air will thus cause cooling of the thermostatic element I29 which will move the switch II8 to a closed position. Upon closure of switch IIB a circuit for energizing and opening the main fuel valve I2 will be completed as follows: from line conductor 38' through thermostatic blade 35, fixed contact 89, wire 40, wire I41, switch IIB, valve I2, wire I48, wire II back to line conductor 39. Assoon as valve I2 opens heating is initiated and proceeds in the same manner as described in connection with Figure 1. Should now at any time there be a failure of the draft within conduit 23 so as to cause the air therein to become more or less stagnant the heat from heater 28 will no longer be carried away and element I29 will not be cooled and it will cause switch H8 to assume open position thereby terminating heating. Upon thermostat 33 becoming satisfied the fan immediately stops and both valves close. 7

From the foregoing it is apparent that the modification of my invention shown in Figure 2 provides a correspondingly inexpensive but effective system for controlling the fuel valve or the like in such a maner that scavenging of the combustion chamber is always assured and moreover that safety of operation which is al= ways a prerequisite of such systems is assured as well.

My invention is particularly adapted to a combustion control system in combination with which I have disclosed it but it is to be understood that it is adaptable to other uses and to use in other combinations and arrangements. Therefore my disclosure is to be interpreted as illustrative only and I am to be limited only as determined by the appended claims.

I claim as my invention:

1. In a control system, in combination, heating means, fuel said heating means, an energizing circuit for said fuel supplying means, draft supplying means for said heating means, means controlling said draft means and a draft responsive device controlling the fuel supply means, said device comprising means forming a passageway arranged to divert draft air from said draft supplying means, a heater and a heat actuated switching means in control of said circuit for said fuel supplying means arranged so that the draft through said passageway carries heat from the heater to the switching means for actuating the switching means to one position, the switching means being actuated to another position when not heated and said passageway forming means being so arranged that air is blown therethrough in one direction when the draft supplying means is operating and air is drawn therethrough in the opposite direction when the draft supplying means is not operating.

-2. In a control system, in combination, heating means, fuel supply means cooperating with said heating means, draft supplying means for said heating means, means controlling said draft means and and a draft responsive device for energizing the fuel supply means only when said draft suppling means is in operation, said device comprising means forming a passageway adapted to havedraft air pass therethrough, a heater arranged in the path of air passing through said passageway and heat actuated switch means responsive to heat from said heater, said heater being so positioned that said draft supply means is effective to cause heat from said heater to be carried away from the switch means tending to cool said switch means and thereby cause energizationof said fuel supplying means.

3. In an air flow responsive apparatus in combination, means forming a continuously open passageway, means for producing a circulation of fluid through said passageway at a substantially constant rate, means comprising a heat actuated device and a heat source in said pasfluid passes supply means cooperating with is passing over said sageway, said device and source being so relatively disposed that said device is substantially unaffected by radiant heat from said heat'source and when said circulation producing means is in operation said fluid passes first over the heat source and then over the device, and said passageway forming. means being so arranged and disposed that when said circulation producing means is not in operation said heat source induces a rising convection circulation of fluid through said passageway forming means with the fluid s first over said device and then the heat source tending to carry heat away from the device, and a control device actuated to one position by said heat actuated device when said first over said heater and then over and to another position when said fluid passes first over saiddevice and then over said heater. the flow of fluid through said passdageway being unafifected by said control desaid device,

i. Ina heating system, in combination, a combustion chamber, a burner positioned to supply fuel to said combustion chamber, a fuel valve in control of flow of fuel to said burner, a blower for supplying air to said combustion chamber to support combustion, a heater positioned to be subject to flow of air from said blower, means including a thermostat in heat transfer relation to said heater for in closed position when no air from said blower heater and for opening said maintaining said fuel valve when no heat is required in said combustion of said blower and actuation of said thermostat v to open said fuel valve.

5. In aheating system, in combination, a-combustion chamber, a burner positioned to supply fuel to said combustion chamber, a fuel valve in control of flow of fuel to said burnenablower for supplying air to said combustion chamber to support combustion, a

including a thermostat in heat transfer relation to said heater for maintaining said fuel valve in closed position when no air from said blower is passing over said heater and for opening said valve when air from said blower is passing over said heater, a condition responsive means in control of said blower for starting operation of said blower to supply substantially full delivery capacity of said blower to said combustion chamber when her and for stopping operation of said blower heater positioned to be. subject to flow of air from said blower, meansheat is required in said combustion cham-;

chamber, and an electric circuit passing in series through said fuel valve, said thermostat and said condition responsive device, whereby a time interval will elapse between the starting of operation of said blower and the opening ofsaid fuel valve but said fuel valve willclose simultaneously with stopping of said blower due to the action of said condition responsive means.

6. In a heating system, in combination, a combustion chamber, a burner positioned to supply fuel to said combustion chamber, a fuel valve in control of the-flow of fuel to said burner, a blower for supplying air to said combustion chamber to support combustion, means forming a passageway having upper and lower ends, the upper end being in communication with saidvblower, said means being so disposed that one end of the passageway is higher than the other end thereof, a heater positioned within the passageway, means in control of said valve including a thermostat located within the passageway at a point between said heater and the lower end of the passageway for maintaining said fuel valve in closed position when no air is passing over said heater due to the action of said blower and for opening said fuel valve when action of said blower transfers heat from said heater to said thermostat.

, MEADE J. MAYNARD. 

